1. Technical Field
The present invention relates to a nanofiber manufacturing apparatus which produces fibers having diameters of submicron order or nanometer order (referred to as nanofibers in this description) by electrostatic stretching, and a method of manufacturing nanofibers.
2. Description of the Related Art
There is a known method of manufacturing filamentous (fibrous) substances containing a resin and having a submicron- or nanometer-scale diameter by making use of electrostatic stretching (electrospinning).
The electrostatic stretching is a method of manufacturing nanofibers. In the method, a solution prepared by dispersing or dissolving a solute such as a resin in a solvent is effused (ejected) into space through a nozzle or the like, and the solution is charged and electrically stretched in flight so that nanofibers are produced.
The following describes the electrostatic stretching more specifically. The solvent gradually evaporates from the charged solution while the solution effused into space is in flight. The volume of the solution in flight thus gradually decreases while the charges imparted to the solution stays in the solution. As a result, the charge density of the solution in flight gradually increases. The solvent ongoingly evaporates and the charge density of the solution further increases, and the solution is explosively stretched into a line when the Coulomb force generated in the solution and repulsive to the surface tension of the solution surpasses the surface tension. This is how the electrostatic stretching occurs. The electrostatic stretching exponentially occurs in space one after another so that nanofibers having diameters of sub-micron orders or nanometer orders are produced.
One of the specific problems with an apparatus for manufacturing nanofibers by such electrostatic stretching is the difficulty of increasing productivity. For example, effusing solution through cylindrical nozzles arranged in a matrix increases a production rate per unit time and unit area so that productivity of nanofibers is increased. However, although the production rate of nanofibers per unit area can be further increased by narrowing intervals between the nozzles, narrower intervals may cause interference of electric fields between adjacent nozzles, which results in defects in generated nanofibers. In order to solve the problem, the apparatus according to JP2008-174867 includes separators which are arranged in a grid pattern among the nozzles and to which alternating voltage is applied so that interference of electric fields is prevented.